Recently, energy saving is very important because the environmental contamination and the shortage of energy resources have become a major problem in a number of fields including oil hydraulic systems. We previously proposed a pump unit driven by an electric motor with intermittent operation. This pump unit achieves electrical energy saving compared with conventional pump units under a wide range of driving condition. However, construction machines and vehicles mainly use an engine as a power source. In this study, we test the intermittent operation of a pump unit driven by an engine, and we achieve automatic engine restart by means of a hydraulic assist. We research an intermittently operated pump unit driven by a gasoline engine and achieve a saving in energy. In addition, we research the effect of accumulator volume and the stability of the engine restart.

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